1. Field of the Invention
The present invention relates to an apparatus and method for a mobile communication system supporting a multimedia service including voice and packet data services, and in particular, to an apparatus and method for effectively receiving a control channel that transmits control information related to transmission of packet data.
2. Description of the Related Art
A conventional mobile communication system, for example, an Interim Standard-2000 (IS-2000), Code Division Multiple Access (CDMA) mobile communication system, chiefly supports a voice service and a low-speed circuit and packet data service. With the development of a communication technology and at the request of users, research has been conducted on a mobile communication system supporting a high-speed packet data service. In particular, an IS-2000 Evolution in Data and Voice (1×EVDV) mobile communication system, has recently attracted public attention, supports not only a voice service but also a high-speed packet data service. In order to realize a mobile communication system capable of supporting a high-speed packet data service as well as a voice service, a receiver capable of handling high-speed packet data is required.
In the 1×EVDV system, several users share the same packet data channel (PDCH) by time division multiplexing (TDM) in order to increase the transmission efficiency of packet data. In such a system, a transmitter transmits various control information for the packet data channel over a packet data control channel (PDCCH) for the same time period. The control information includes destination address, data rate, modulation scheme and code rate of transmission data, and is used for reception of a packet data channel.
A packet data channel and a packet data control channel both support a plurality of data rates. The data rates are related to a period, or the number of time slots, required for transmitting data having a predetermined length. For example, a length of control information transmitted over a packet data control channel is fixed to 13 bits, and the control information is transmitted over 1, 2 or 4 time slots each having a predetermined length. Although a data rate of a packet data channel can be determined by a data rate of a packet data control channel, a transmitter does not separately inform a receiver of a data rate of the packet data control channel. The receiver detects a data rate of received data from the received data, and acquires control information according to the detected data rate.
As stated above, since a packet data control channel and a packet data channel are simultaneously transmitted in a pair, data transmitted over the packet data channel must be buffered until demodulation on the packet data control channel is completed. Therefore, as demodulation on the packet data control channel is completed earlier, a demodulation start time for the packet data channel is advanced, contributing to rapid demodulation of packet data. That is, in a system that simultaneously transmits a packet data channel and a packet data control channel, demodulation on the packet data control channel must be rapidly performed in order to reduce time delay up to a demodulation start time for the corresponding packet data channel. Accordingly, there is a need for a method for rapidly and accurately demodulating a packet data control channel, especially for a high-speed packet data service.